Scintillating materials can be described as materials that fluoresce when in the presence of high energy electromagnetic radiation (e.g., gamma, X-ray, and so forth). The mechanism in which these materials are able to achieve this phenomenon is attributed to their ability to absorb electromagnetic radiation having a wavelength greater than that of the visible spectrum and releasing the energy with a wavelength that is within the visible spectrum. This property, which can be referred to as a Stokes-Shifting, is indicative of scintillators such as bismuth germinate (BGO), thallium doped sodium iodide (NaI:Th), and cerium-doped yttrium aluminum garnet (Ce:YAG).
The performance of scintillating materials, or scintillators, is generally measured via their efficiency, decay time, stopping power, and energy resolution. To be more specific, efficiency is described as the scintillator's overall ability to convert high-energy radiation (e.g., gamma radiation) into visible light. Efficiency is measured in light output (LO), which is sometimes referred to as light yield (LY), or even scintillation output, having the units of photons per megaelectronvolts (Photons/MeV). Decay time is the amount of time over which a scintillator releases stored energy as visible light, which is also referred to as the response of the scintillator. The decay time of scintillators can vary from nanoseconds to microseconds. Generally, it is desirable that the decay time is rapid (e.g., normally expressed in nanoseconds).
In gamma ray spectroscopy, the energy resolution of a scintillator is defined as its ability to discriminate between gamma rays with slightly different energies. The energy resolution is defined as the Full Width at Half Maxima (FWHM) of the photopeak at a given energy.
Depending upon these properties, specific scintillators can be employed in a variety of applications, such as in radioisotope imaging devices, radiation detectors (e.g., gamma detectors, X-ray detectors, and so forth), positron emission tomography equipment, and so on. However, commercial scintillators such as BGO, (NaI:Tl) and (Ce:YAG) exhibit several notable shortcomings in such applications. For example, BGO and Ce:YAG scintillators exhibit poor light output (e.g., about 9,000 photons/MeV) and energy resolution when irradiated with gamma rays. Therefore these materials are not preferred in equipment and devices that operate with respect to gamma radiation. For this reason, many such devices employ NaI:Tl scintillators, which exhibit greater energy resolution (e.g., about 7% greater) than the BGO and Ce:YAG scintillators, but provide less than desirable energy resolution. In another example, it has been found that BGO exhibits generally slower decay times than NaI:Tl and Ce:YAG scintillators in applications such as computed tomography (CT) scanners. Yet even further, it has been found that due to the relatively low atomic number of Ce:YAG, this scintillator's stopping power is less than desired. As a result, larger crystals are required for applications that employ this material, which can result in higher cost and size.
Due to these shortcomings, as well as others, there remains an unmet need in the art for scintillators having enhanced light output and energy resolution from gamma ray irradiation.